Message ID | 20190809010837.24166-1-miles.chen@mediatek.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [RFC,v2] mm: slub: print kernel addresses in slub debug messages | expand |
On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com wrote: > Possible approaches are: > 1. stop printing kernel addresses > 2. print with %pK, > 3. print with %px. No. The point of obscuring kernel addresses is that if the attacker manages to find a way to get the kernel to spit out some debug messages that we shouldn't leak all this extra information. > 4. do nothing 5. Find something more useful to print. > INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) ... you don't have any randomness on your platform? > INFO: Object 0x(____ptrval____) @offset=1408 fp=0x(____ptrval____) > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 > Redzone (____ptrval____): bb bb bb bb bb bb bb bb > Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > ... > FIX kmalloc-128: Object at 0x(____ptrval____) not freed But if you have randomness, at least some of these "pointers" are valuable because you can compare them against "pointers" printed by other parts of the kernel. > After this patch: > > INFO: Slab 0xffffffbf00f57000 objects=25 used=23 fp=0xffffffc03d5c3500 > INFO: Object 0xffffffc03d5c3500 @offset=13568 fp=0xffffffc03d5c0800 > Redzone 00000000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000020: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000030: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000040: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000050: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000060: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Redzone 00000070: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb > Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000040: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000050: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000060: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b > Object 00000070: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 > Redzone 00000000: bb bb bb bb bb bb bb bb > Padding 00000000: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding 00000010: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding 00000020: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > Padding 00000030: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a > ... > FIX kmalloc-128: Object at 0xffffffc03d5c3500 not freed It looks prettier, but I'm not convinced it's more useful. Unless your platform lacks randomness ...
On Thu, 2019-08-08 at 19:46 -0700, Matthew Wilcox wrote: > On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com wrote: > > Possible approaches are: > > 1. stop printing kernel addresses > > 2. print with %pK, > > 3. print with %px. > > No. The point of obscuring kernel addresses is that if the attacker manages to find a way to get the kernel to spit out some debug messages that we shouldn't > leak all this extra information. got it. > > > 4. do nothing > > 5. Find something more useful to print. agree > > > INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) > > ... you don't have any randomness on your platform? We have randomized base on our platforms. > But if you have randomness, at least some of these "pointers" are valuable > because you can compare them against "pointers" printed by other parts > of the kernel. Understood. Keep current %p, do not leak kernel addresses. I'll collect more cases and see if we really need some extra information. (maybe the @offset in current message is enough) thanks for your comments!
On Fri, Aug 09, 2019 at 10:11:58PM +0800, Miles Chen wrote: > On Thu, 2019-08-08 at 19:46 -0700, Matthew Wilcox wrote: > > On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com wrote: > > > INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) > > > > ... you don't have any randomness on your platform? > > We have randomized base on our platforms. Look at initialize_ptr_random(). If you have randomness, then you get a siphash_1u32() of the address. With no randomness, you get this ___ptrval___ string instead.
On Fri, 2019-08-09 at 07:26 -0700, Matthew Wilcox wrote: > On Fri, Aug 09, 2019 at 10:11:58PM +0800, Miles Chen wrote: > > On Thu, 2019-08-08 at 19:46 -0700, Matthew Wilcox wrote: > > > On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com wrote: > > > > INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) > > > > > > ... you don't have any randomness on your platform? > > > > We have randomized base on our platforms. > > Look at initialize_ptr_random(). If you have randomness, then you > get a siphash_1u32() of the address. With no randomness, you get this > ___ptrval___ string instead. > You are right. There is no randomness in this platform. (I ran my test code on Qemu with no randomness) thanks again
On 8/9/19 4:46 AM, Matthew Wilcox wrote: > On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com wrote: >> Possible approaches are: >> 1. stop printing kernel addresses >> 2. print with %pK, >> 3. print with %px. > > No. The point of obscuring kernel addresses is that if the attacker manages to find a way to get the kernel to spit out some debug messages that we shouldn't > leak all this extra information. On the other hand, while CONFIG_SLUB_DEBUG=y is common, the actual checks and printing happens when the (relatively expensive) checks are actually enabled during boot, i.e. during a debugging session, not production defaults. I can see how knowing the exact address might be useful when e.g. a crash dump is also taken. I would say %pK would be a good fit, if kptr_restrict also had a setting that makes %pK behave like %px (looks like it doesn't), so that setting would be enabled in such a debugging session. >> 4. do nothing > > 5. Find something more useful to print. > >> INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) > > ... you don't have any randomness on your platform? > >> INFO: Object 0x(____ptrval____) @offset=1408 fp=0x(____ptrval____) >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> ... >> FIX kmalloc-128: Object at 0x(____ptrval____) not freed > > But if you have randomness, at least some of these "pointers" are valuable > because you can compare them against "pointers" printed by other parts > of the kernel. > >> After this patch: >> >> INFO: Slab 0xffffffbf00f57000 objects=25 used=23 fp=0xffffffc03d5c3500 >> INFO: Object 0xffffffc03d5c3500 @offset=13568 fp=0xffffffc03d5c0800 >> Redzone 00000000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000020: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000030: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000040: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000050: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000060: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000070: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000040: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000050: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000060: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000070: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 >> Redzone 00000000: bb bb bb bb bb bb bb bb >> Padding 00000000: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000010: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000020: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000030: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> ... >> FIX kmalloc-128: Object at 0xffffffc03d5c3500 not freed > > It looks prettier, but I'm not convinced it's more useful. Unless your > platform lacks randomness ... >
diff --git a/mm/slub.c b/mm/slub.c index 8834563cdb4b..bc1fb8e81557 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -528,7 +528,7 @@ static void print_section(char *level, char *text, u8 *addr, unsigned int length) { metadata_access_enable(); - print_hex_dump(level, text, DUMP_PREFIX_ADDRESS, 16, 1, addr, + print_hex_dump(level, text, DUMP_PREFIX_OFFSET, 16, 1, addr, length, 1); metadata_access_disable(); } @@ -611,7 +611,7 @@ static void print_tracking(struct kmem_cache *s, void *object) static void print_page_info(struct page *page) { - pr_err("INFO: Slab 0x%p objects=%u used=%u fp=0x%p flags=0x%04lx\n", + pr_err("INFO: Slab 0x%px objects=%u used=%u fp=0x%px flags=0x%04lx\n", page, page->objects, page->inuse, page->freelist, page->flags); } @@ -653,7 +653,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p) print_page_info(page); - pr_err("INFO: Object 0x%p @offset=%tu fp=0x%p\n\n", + pr_err("INFO: Object 0x%px @offset=%tu fp=0x%px\n\n", p, p - addr, get_freepointer(s, p)); if (s->flags & SLAB_RED_ZONE) @@ -991,7 +991,7 @@ static void trace(struct kmem_cache *s, struct page *page, void *object, int alloc) { if (s->flags & SLAB_TRACE) { - pr_info("TRACE %s %s 0x%p inuse=%d fp=0x%p\n", + pr_info("TRACE %s %s 0x%px inuse=%d fp=0x%p\n", s->name, alloc ? "alloc" : "free", object, page->inuse, @@ -1212,7 +1212,7 @@ static noinline int free_debug_processing( slab_unlock(page); spin_unlock_irqrestore(&n->list_lock, flags); if (!ret) - slab_fix(s, "Object at 0x%p not freed", object); + slab_fix(s, "Object at 0x%px not freed", object); return ret; } @@ -3693,7 +3693,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page, for_each_object(p, s, addr, page->objects) { if (!test_bit(slab_index(p, s, addr), map)) { - pr_err("INFO: Object 0x%p @offset=%tu\n", p, p - addr); + pr_err("INFO: Object 0x%px @offset=%tu\n", p, p - addr); print_tracking(s, p); } }